Rail systems utilize the same tracks for two way traffic. Trackside signals indicating various track conditions are used by engineers, dispatchers, and computerized control systems to control access to the tracks and prevent conflicting train movements. Switches placed throughout the rail system divert traffic from the main track to side tracks (sidings) allowing trains to pass one another or to change the train's route. Switches are also utilized in rail yards to change the train's route. At the switch, the rails of the track are mechanically moved to successfully divert the train to the new track. The locomotive engineer visually monitors track signals located trackside to determine the status of the track switches and to obtain authority to enter a specific track section and takes action, for instance adjusting the speed of the train when signals indicate the train will be diverted to a siding due to switch positions. Since safety-critical decisions are made based on the status of the switches and signals, a system and method are needed to ensure that any signal and switch status is reported correctly. Due to the potential for operator error, it is beneficial for railroads to electronically verify the status of switches and signals along the track by communicating the status of these signals to a system on-board the locomotive. Based on the information received, the on-board system can monitor the speed and location of the train and override the engineer by, for example, applying the brakes if the train's authorized speed profile is in danger of being exceeded. Those of skill in the art will recognize that this system of electronically monitoring and controlling train movements to provide increased rail safety is commonly referred to as Positive Train Control.
Railroad signaling systems include complex interlockings which are arrangements of signaling apparatus (e.g. relays, software logic, etc.) that prevent conflicting train movements through an arrangement of tracks. By way of example, some of the fundamental principles of interlocking include: signals may not be operated to permit conflicting train movements to take place at the same time; switches in a route must be properly ‘set’ (in position) before a signal may allow train movements to enter that route; once a route is set and a train is given a signal to proceed over that route, all switches in the route are locked in position until either the train passes out of the portion of the route affected, or the signal to proceed is withdrawn and sufficient time has passed to ensure that a train approaching that signal has had opportunity to come to a stop before passing the signal. Interlockings can be categorized as mechanical, electrical (relay-based), or electronic (software-based).
Trackside input electrical components such as switch contacts and hazard detectors are electrically connected to the interlocking and provide track condition information as inputs to the interlocking. When the input electrical component needs to provide an input to the interlocking, voltage is applied to the connection or a contact closes a circuit, thereby sending a track condition input to the interlocking. The interlocking processes the multiple track condition inputs it receives and determines track status. The interlocking is electrically connected to output electrical components such as signals. The interlocking identifies the output electrical components to be energized based on the track status, and applies voltage to the connection between the interlocking and the particular output electrical components.
The prior art verification system for reporting the status of switches and signals to a remote train control system to confirm visual signals comprises a trackside central control unit with its own independent power supply and microprocessor. The central control unit is electrically connected via wiring or some similar physical method to each of a plurality of trackside electrical components, and can sense a combination of electrical voltages and currents in these components. The microprocessor of the central control unit continuously monitors the electrical components to measure their electric current and/or voltage and determines track conditions such as which signal lamps are on, the positions of switches, and the state of any other hazard detectors. It is critical in the prior art system that these electric measurements are correct. There are many outside influences such as lightning strikes, electrical surges, etc., that could effect the accuracy of the electric measurements. For this reason, the central control unit includes many additional, and often redundant, components such as duplicate sensors, multi-path processors, redundant input circuits and board, dual processing boards and additional software to ensure the accuracy of the electric readings. These prior art central control units are expensive due, in large part, to the additional components and software needed to ensure the accuracy of the electric readings.
One disadvantage of the prior art system is that it requires expensive, safety-validated software for the microprocessor and significant testing to ensure that all failure modes have been addressed. Maintaining such a software development process for the lifetime of the product burdens it with significant cost. A second disadvantage of the existing system is that the microprocessor is centrally mounted in a trackside bungalow, and a significant amount of wiring is needed to reach the various sensing points. This adds cost to the deployment into existing bungalows.
It is an objective of the present invention to provide a fail safe voltage sensor for verifying the status of trackside signals and switches in safety-critical railroad applications which eliminates the need for duplicative components to account for all potential errors and failures. Another objective of the present invention is to provide a cost effective, single input sensor to replace more expensive, multi-input equipment used in prior art systems. Another objective of the present invention is to provide a sensor with low power consumption which allows for longer battery life of the overall trackside control system. The trackside installations including the trackside signals and switches, the interlocking, the central control unit and other components are typically powered by a bank of batteries located at the trackside installation. Yet another objective is to provide a voltage sensor which can be installed near to each electrical component to be sensed thereby greatly reducing the amount of wiring needed to connect the prior art multi-input systems to each electrical component and the cost of installing and testing these large lengths of wire.